This invention relates to a waterproof box-like casing, and more particularly to a waterproof box-like casing suited for housing an electronic unit or the like within an engine room of a vehicle.
An object to be waterproofed is received within a box-like body of a waterproof box-like casing having an opening, and then this opening is hermetically closed by a lid, and then the casing is mounted at a predetermined position. With a simple box-like sealed construction, however, the hermetic condition can not always be maintained in an environment in which the temperature abruptly changes. For example, a waterproof box-like casing holds an engine-control electronic equipment therein, and is mounted within an engine room. The interior of the engine room is liable to increase in temperature. When water is splashed on the waterproof casing during the running, the temperature drops abruptly. As a result, the atmospheric pressure within the casing decreases in accordance with the temperature change, and therefore a strain develops in the casing, so that the water intrudes through a gap around the lid of the hermetic construction.
Therefore, conventionally, as disclosed in Japanese Utility Model Unexamined Publication Nos. 56-112978 and 57-186094, a waterproof box-like casing has not been of a sealed construction, and instead a vent hole has been formed in the casing so as to make the inside and outside of the casing equal in atmospheric pressure to each other. In the construction shown in the former publication, the vent hole is in the form of a labyrinth, and moisture is held in the labyrinth when the outside air flows into the casing. In the construction shown in the latter publication, the vent hole is covered by an auxiliary plate to provide a staggered vent passage so that the water will not immediately intrude.
The above-mentioned conventional waterproof box-like casings have the following problems.
Namely, in the former, when an amount of the water which is greater than the water being able to be held in the labyrinth-like vent hole is drawn together with the outside air, this water intrudes into the interior. In the latter, the vigorously splashed water will inevitably intrude into the casing.
The present invention has been made in view of the above problems, and an object of the invention is to provide a waterproof box-like casing which can provide a good waterproof effect even in an environment in which a temperature change is vigorous.